Sarcomatoid carcinoma

Sarcomatoid carcinoma is a type of cancer that contains features of both carcinoma and sarcoma. Carcinomas are cancers that start in epithelial cells, which line the surface of organs, while sarcomas are cancers that start in mesenchymal cells, such as those found in connective tissue, bone, or muscle. In sarcomatoid carcinoma, the tumour starts as a carcinoma but has areas where the cancer cells have changed in appearance and now look more like spindle cells, which resemble the cells typically seen in sarcomas.

This type of cancer is considered aggressive and may grow and spread more quickly than typical carcinomas.

Where can sarcomatoid carcinoma occur?

Sarcomatoid carcinoma can occur in many parts of the body, most commonly in organs where carcinomas are already common.

These include:

• Lungs (sarcomatoid carcinoma of the lung or pleura).

• Kidneys (sarcomatoid renal cell carcinoma).

• Bladder and urinary tract.

• Esophagus and gastrointestinal tract.

• Liver or bile ducts.

• Skin or soft tissues.

In each of these locations, sarcomatoid carcinoma represents a variant or subtype of a more common carcinoma that has undergone sarcomatoid transformation.

Why is sarcomatoid carcinoma important?

Sarcomatoid carcinoma is important because it is typically a high-grade tumour, which means:

• The cancer cells look very abnormal under the microscope.

• It tends to grow and spread more quickly than typical carcinomas.

• It may respond differently to treatment, especially chemotherapy or immunotherapy.

Identifying sarcomatoid features in a tumour helps guide treatment decisions and gives doctors a better understanding of the prognosis.

What does sarcomatoid carcinoma look like under the microscope?

Under the microscope, sarcomatoid carcinoma contains two types of cancer cells:

• Epithelial cells, which resemble those found in more typical carcinomas (such as gland-forming or squamous cells).

• Spindle-shaped cells, which resemble the cells seen in sarcomas (elongated, often arranged in bundles or sheets).

These spindle cells often lack the structure of normal epithelial cells and may look very aggressive. In some cases, giant cells, areas of necrosis (cell death), or high numbers of dividing cells (mitoses) may also be seen.

How is sarcomatoid carcinoma diagnosed?

The diagnosis is usually made by examining a biopsy or surgical specimen under the microscope. Pathologists often use immunohistochemistry, a special type of staining, to help confirm the diagnosis. These tests detect proteins found in epithelial cells (such as cytokeratins) and help distinguish sarcomatoid carcinoma from true sarcomas or other types of cancer.

In some cases, molecular testing may be done to look for specific genetic changes that can guide treatment.

Is sarcomatoid carcinoma the same as sarcoma?

No. Although the word “sarcomatoid” means “like a sarcoma,” sarcomatoid carcinoma is not a true sarcoma. It is a type of carcinoma that has changed in appearance to resemble a sarcoma. This distinction is important because treatment and prognosis differ between sarcomas and sarcomatoid carcinomas.

Questions to ask your doctor

• What organ did the sarcomatoid carcinoma develop in?

• How advanced is the tumour (stage)?

• What treatments are recommended for this type of cancer?

• Was immunohistochemistry or genetic testing used to confirm the diagnosis?

• How does sarcomatoid carcinoma affect my prognosis?